Apparatus, system and method of forming polymer microspheres for use in additive manufacturing

ABSTRACT

The embodiments are and include at least an apparatus, system and method for forming print material particles for additive manufacturing (AM) printing. The apparatus, system and method include at least a melt chamber comprising a polymer melt; a vertical extruder that fluidically receives the polymer melt; an atomizer that atomizes the polymer melt from the vertical extruder and that distributes the atomized polymer melt; a fall chamber comprising a plurality of zones into which the atomized polymer melt is distributed; and a collector to receive the print material particles formed of the atomized polymer melt after falling through the plurality of zones.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority of U.S.application Ser. No. 16/871,824, filed May 11, 2020, as acontinuation-in-part, to International Application No.PCT/US2019/065035, filed Dec. 6, 2019, which claims the benefit ofpriority to U.S. Provisional Application No. 62/776,287, filed Dec. 6,2018, entitled: “Apparatus, System and Method of Forming PolymerMicrospheres For Use In Additive Manufacturing,” the entirety of each ofwhich applications is incorporated herein by reference as if set forthin its respective entirety.

BACKGROUND Field of the Disclosure

The present disclosure relates to additive manufacturing, and, morespecifically, to an apparatus, system and method of forming polymermicrospheres for use in additive manufacturing.

Description of the Background

Three-dimensional (3D) printing is any of various processes in whichmaterial is joined or solidified under computer control to create athree-dimensional object. The 3D print material is “added” onto a base,such as in the form of added liquid molecules or layers of powder grainor melted feed material, and upon successive fusion of the printmaterial to the base, the 3D object is formed. 3D printing is thus asubset of additive manufacturing (AM).

A 3D printed object may be of almost any shape or geometry, andtypically the computer control that oversees the creation of the 3Dobject executes from a digital data model or similar additivemanufacturing file (AMF) file. Usually this AMF is executed on alayer-by-layer basis, and may include control of other hardware used toform the layers, such as lasers or heat sources.

There are many different technologies that are used to execute the AMF.Exemplary technologies may include: fused deposition modeling (FDM);stereolithography (SLA); digital light processing (DLP); selective lasersintering (SLS); selective laser melting (SLM); inkjet printmanufacturing (IPM); laminated object manufacturing (LOM); andelectronic beam melting (EBM).

Some of the foregoing methods melt or soften the print material toproduce the print layers. For example, in FDM, the 3D object is producedby extruding small beads or streams of material which harden to formlayers. A filament of thermoplastic, wire, or other material is fed intoan extrusion nozzle head, which typically heats the material and turnsthe flow on and off.

Other methods, such as laser or similar beam-based techniques, may ormay not heat the print material, such as a print powder, for the purposeof fusing the powder granules into layers. For example, such methodsmelt the powder using a high-energy laser to create fully densematerials that may have mechanical properties similar to those ofconventional manufacturing methods. Alternatively, SLS, for example,uses a laser to solidify and bond grains of plastic, ceramic, glass,metal or other materials into layers to produce the 3D object. The lasertraces the pattern of each layer slice into the bed of powder, the bedthen lowers, and another layer is traced and bonded on top of theprevious.

In contrast, other methods, such as IPM, may create the 3D object onelayer at a time by spreading a layer of powder, and printing a binder inthe cross-section of the 3D object. This binder may be printed using aninkjet-like process.

Currently, the known art typically produces powders for additivemanufacturing using methods that are slow, inefficient, and whichrequire significant effort. The foregoing notwithstanding, it is typicalthat such known processes produce print material that varies greatly insize and density, and which generally lack the sphericity needed formore refined print processes. Worse yet, such powder forming methods arenot only exhaustive, expensive and inefficient, but are also often printmaterial-specific. That is, the methods and materials used are varied inthe known art in direct accordance with the desired composition of theprint material to be produced.

SUMMARY

The embodiments are and include at least an apparatus, system and methodfor forming print material particles for additive manufacturing (AM)printing. The apparatus, system and method may include at least a meltchamber comprising a polymer melt; a vertical extruder that fluidicallyreceives the polymer melt; an atomizer that atomizes the polymer meltfrom the vertical extruder and that distributes the atomized polymermelt; a fall chamber comprising a plurality of zones into which theatomized polymer melt is distributed; and a collector to receive theprint material particles formed of the atomized polymer melt afterfalling through the plurality of zones.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed non-limiting embodiments are discussed in relation to thedrawings appended hereto and forming part hereof, wherein like numeralsindicate like elements, and in which:

FIG. 1 is an illustration of an additive manufacturing printing system;

FIG. 2 illustrates an exemplary print material;

FIG. 3 illustrates print particle formation;

FIG. 4 illustrates aspects of the embodiments;

FIG. 5 illustrates aspects of the embodiments;

FIG. 6 shows a vessel that can be utilized for forming polymermicrospheres;

FIG. 7 illustrates additive manufacturing printing; and

FIG. 8 illustrates an exemplary computing system.

DETAILED DESCRIPTION

The figures and descriptions provided herein may have been simplified toillustrate aspects that are relevant for a clear understanding of theherein described apparatuses, systems, and methods, while eliminating,for the purpose of clarity, other aspects that may be found in typicalsimilar devices, systems, and methods. Those of ordinary skill may thusrecognize that other elements and/or operations may be desirable and/ornecessary to implement the devices, systems, and methods describedherein. But because such elements and operations are known in the art,and because they do not facilitate a better understanding of the presentdisclosure, for the sake of brevity a discussion of such elements andoperations may not be provided herein. However, the present disclosureis deemed to nevertheless include all such elements, variations, andmodifications to the described aspects that would be known to those ofordinary skill in the art.

Embodiments are provided throughout so that this disclosure issufficiently thorough and fully conveys the scope of the disclosedembodiments to those who are skilled in the art. Numerous specificdetails are set forth, such as examples of specific components, devices,and methods, to provide a thorough understanding of embodiments of thepresent disclosure. Nevertheless, it will be apparent to those skilledin the art that certain specific disclosed details need not be employed,and that embodiments may be embodied in different forms. As such, theembodiments should not be construed to limit the scope of thedisclosure. As referenced above, in some embodiments, well-knownprocesses, well-known device structures, and well-known technologies maynot be described in detail.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. For example, asused herein, the singular forms “a”, “an” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The steps, processes, and operations described herein are notto be construed as necessarily requiring their respective performance inthe particular order discussed or illustrated, unless specificallyidentified as a preferred or required order of performance. It is alsoto be understood that additional or alternative steps may be employed,in place of or in conjunction with the disclosed aspects.

When an element or layer is referred to as being “on”, “engaged to”,“connected to” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present, unless clearlyindicated otherwise. In contrast, when an element is referred to asbeing “directly on,” “directly engaged to”, “directly connected to” or“directly coupled to” another element or layer, there may be nointervening elements or layers present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.). Further, as used herein the term “and/or” includes anyand all combinations of one or more of the associated listed items.

Yet further, although the terms first, second, third, etc. may be usedherein to describe various elements, components, regions, layers and/orsections, these elements, components, regions, layers and/or sectionsshould not be limited by these terms. These terms may be only used todistinguish one element, component, region, layer or section fromanother element, component, region, layer or section. Terms such as“first,” “second,” and other numerical terms when used herein do notimply a sequence or order unless clearly indicated by the context. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the embodiments.

The disclosed apparatus, system and method provide additivemanufacturing materials, and enable the production of additivelymanufactured parts from those materials, having properties presentlyunavailable in the known art. Further, embodiments include designs forspecification that may match and/or correlate particular printmaterials, print material fillers, and printed output objects given oneor more processes available to produce the printed output object.

Historically, the use of additive manufacturing (AM), such as 3Dprinting, to produce parts having varying densities, such as a lowdensity foam part, has been challenging and required custom machines andcustomized matching of materials. Contrary to the known art, theembodiments include materials and processes by which material isproduced to more readily be used in existing AM technologies to produceparts of variable densities for various industries.

The embodiments may allow for a part to be printed from the providedprint materials, and then selectively cut, crushed, or otherwiseprocessed to create a final part. The part produced using AM can beprinted very rapidly using existing AM printing technologies. Further,the inherent elastomeric properties of certain parts are morecontrollable throughout the printed part in the disclosed embodiments,due to the print material formation, and can thus be further tailoredduring and after the printing, than the known art.

FIG. 1 illustrates a typical additive manufacturing (AM) system 10. Inthe illustration, a print material 12 is fed into a print process 14,such as the powder/pulverant-based AM processes discussed throughout,and the print process 14 outputs a printed 3D part 16. In theembodiments, the print material 12 may have the particularcharacteristics discussed herein, which may allow for the use of theprint material 12 in any one or more processes 14, and which therebyresult in any of various types of output parts 16 such as may have thecharacteristics discussed herein.

Additionally, computing system 1100 may execute one or moreprograms/algorithms 1190 to control one or more aspects of system 10, asreferenced throughout. By way of example, program 1190 may be the AMFreferenced herein above, and the AMF 1190 may independently control atleast process 14. The AMF may additionally control the selection and/ordistribution of print material 12, compounds 12 a, and/or additives andfillers, and may further modify processes 14, print materials 12, and soon in order to achieve a user-desired print output 16, as discussedfurther herein below.

More particularly, the embodiments may include specificallypolymer-based print materials 12. These materials 12 may include aTPU-based microsphere, for example, and may additionally include one ormore additives 20, such as may further enhance the operatingcharacteristics and print operating windows discussed throughout thedisclosure, and such as are discussed further herein below.

That is, the embodiments allow for the addition of additives, such asusing unique screw extruders to melt the incoming material(s), sometimesfrom multiple material sources. That is, the use of an extruder allowsnot only homopolymers to be melt-atomized, but also allows for the samemelt-atomization with any ones of a near infinite amount of additives(an “additive” being defined to include anything other than the polymer)introduced immediately prior to atomization. By way of non-limitingexample, reinforcement and filler additives, such as fibers, may beadded via a twin screw extruder, melt-mixed, atomized, and solidified,all with the resin/filler ratio maintained in the resulting particle(e.g., the additive may still be encapsulated/surrounded by polymer). Assuch, melting/mixing/atomization/particle collection in anadditive-inclusive method may nevertheless all be performed by thesingle disclosed system.

As referenced, the disclosed print input materials 12 may be used inpowder-based AM processes 14, such as those in which the powder 120including the material 12 may be spread, melted in a targeted manner,and/or allowed to or processed to solidify, thus forming successivelayers that result in a three-dimensional output object/part 16 havingthe characteristics discussed herein as indicative of both the process14 and the input print material 12. Processes 14 may include, but arenot limited to: Selective Laser Sintering (SLS), Selective Laser Melting(SLM), Selective Heat Sintering (SHS), High Speed Sintering (HSS), MultiJet Fusion (MJF), Binder Jetting (BJ), Material Jetting (MJ), LaminatedObject Manufacturing (LOM), and other AM technologies referenced herein,and/or AM technologies that utilize thermoplastic powders/pulverants asmay be known to the skilled artisan. It will also be understood to theskilled artisan that other AM and similar processes 14 may be modifiedto employ the print materials 12 disclosed herein, including but notlimited to injection molding, roto molding, vacuum molding, subtractivemanufacturing, and so on.

As referenced above, and referring now specifically to FIG. 2, additives130 may be included with material 12 in forming powder 120. Additives130 may provide desired characteristics to powder 120, may enable orimprove aspects of processes 14, or may provide desired characteristicsto output part 16 produced by exposure of the input print material 12 toprocess 14. Moreover, additives 130 may enable the particularcharacteristics of input print material 12 discussed herein. Additives130 may include, by way of non-limiting example, glass beads, glassfibers, carbon fibers, carbon black, metal oxides, copper metals, flameretardants, antioxidants, pigments, powder flow aids, inks, and so on.For example, ink additives 130 may allow for modification of printmaterial 12 properties, such as may provide for different functionalinks for use in multi-jet fusion AM printing.

More particularly, the disclosure includes AM “printed” output objects16 that are printed from print material 12. As referenced above withrespect to FIG. 2, such a print material 12 may be formed of combinedparticles having combination chemical makeups in melt 1304 discussedbelow. The combination print material 12 may provide a variability inthe density of the print material 12, and hence in the AM printed output16.

Particles having a combination chemical makeup 12 may necessitate asolvent during particle formation, and the solvent may be, for example,a liquid or gas that serves as the medium for a chemical reaction. Thesolvent may be non-participatory with the reactants in a solution,wherein the solvent does not participate in the reaction; orparticipatory, wherein the solvent may be, for example an acid (proton),a base (removing protons), or a nucleophile (donating a lone pair ofelectrons), and may thereby contribute to the chemical reaction.

For different applications, the melt material 1304 may vary inaccordance with the application in the disclosed embodiments. That is,the melt 1304 detailed below may have a combination chemical makeup, ormay consist of solely polymer 1306. For example, foam-centricapplications may require formation of an elastomeric print material 12having high elongation, substantial rebound, and adequate compression.Applicable elastomeric compounds in the disclosed processes may thusinclude: styrene block copolymers, thermoplastic olefins, elastomericalloys, thermoplastic polyurethanes, thermoplastic copolyesters,thermoplastic polyamides, ethylene-vinyl acetate, ethylene propylenerubber, ethylene propylene diene rubber, polyurethanes, silicones,polysulfides, elastolefins, high density polyethylene, low densitypolyethylene, linear low density polyethylene, polypropylene, polyolefincopolymers, polystyrene, polystyrene copolymers, polyacrylates,polymethacrylates, polyesters, polyvinylchloride, fluoropolymers, liquidcrystal polymers, polyamides, polyether imides, polyphenylene sulfides,polysulfones, polyacetals, polycarbonates, polyphenylene oxides,polyurethanes, thermoplastic elastomers, epoxies, alkyds, melamines,phenolics, ureas, vinyl esters, liquid crystal polymers and/orcombinations thereof.

The embodiments provide improved methods of producing polymer powders120 using the aforementioned polymer melt 1304. Particularpolymer-centric powders 120 may necessitate the use, in melt 1304 ratherthan as powder additives 130, of melt-processed reinforcements or otheradditives that do not generally allow for the use of the liquid orgas-based processes of the known art. The known art for producingpolymer powders 120 for additive manufacturing (AM) systems generallyconsists of precipitation and/or compounding-grinding-polishing. Thatis, the known art necessitates a multi-step process to form powders 120of particles 12 having combination chemical makeups, which isinefficient, and which leads to poor results, at least in that thegreater the number of process steps that must be controlled, the greatthe number of process points at which errors can be introduced. Theembodiments allow for the production of powders 120 having complexparticles 12 in a single-step, single machine process, and areapplicable to wide range of both neat and reinforced/modified polymers.

That is, aspects of the embodiments may provide an apparatus, system andmethod for mass production of high-quality spherical powders, and highaspect ratio microfibers, from molten polymers, such as for use as aprint material in AM printing processes. The polymer melt is fed, suchas from an extruder, into an atomizer for distribution of the atomizedpolymer melt into a fall chamber having a plurality of controlled zones.

For example, a high-pressure non-reactive gas, such as a nitrogen gas inthe range of 7.6 MPa/1050 psi, may force the extruded polymer meltthrough an atomizer such that the molten polymer is forced into finedroplets that cool through the multiple zones to form spherical powderparticles. Polyethylene-based powders, such as ranging in size fromabout 0.1 μm to about 200 μm, may thereby be efficiently produced inshort cycle times by exerting control over several process variables,such as atomization temperature, the polymer melt stream size, the fallrate, and the process zones. By way of non-limiting example, a maximumweight fraction of the powder at 0-53 μm may be produced, such as byatomizing a 3.175-mm melt stream size at, by way of example, a range of205° C.

Such zones may be flow, heat, or collection zones, by way of example.More specifically, heat may be selectively controlled in theembodiments, such as in bands or zones. Each of a plurality of heatzones may hold material at a specific temperature as the material fallsor otherwise passes through that zone. This control of the temperatureaxially along chamber may be indirect, such as using heater bands.Direct heating zones may be created by heating the gas inlet to thechamber at different points or stages of the chamber, such as throughthe use of gas pre-heating. This gas pre-heating may utilize theaforementioned heater bands to pre-heat the gas in an externalcontainment chamber.

More particularly and as illustrated in FIG. 3, a process chamber 1300in accordance with the embodiments may include, at an upper portionthereof, a vertical extruder or other vessel 1302 that contains apolymer melt 1304. By way of example, the polymer 1306 may enter theextruder or vessel 1302 as a pellet or other raw material state, and isthen heated at least to its respective melt point to obtain a suitableviscosity of the melt 1304 for processing.

More specifically, the vessel 1302 containing the polymer 1306 may beheated, such as by heater 1310, past the respective Tm of that polymer1306, after which a valve 1312 at the base of the vessel 1302 may beopened to allow the polymer melt 1304 to flow gravimetrically.Alternatively, the polymer 1306 may be melted in the vessel 1302, andmay be pressurized to flow, such as through the atomizer 1320 referencedbelow. In this case, the flow path for the atomized melt may be heatedin order to maintain the polymer melt 1304 in a molten state. Yetfurther and alternatively, a single or twin screw extruder 1322 may bemounted vertically atop the atomizer 1320 discussed below, and thepolymer melt 1304 may be heated and compounded with various additives,such as to be alloyed, reinforced, or otherwise modified to a specificformulation, and the melt 1304 may then exit through a die.

The melt 1304 may be extruded or otherwise passed to atomizer 1320 thatatomizes the melt 1304 a into a given particle size. The atomizer 1320may be or include at least one of a centrifugal, a spinning/choppingdisc, or gas (which may include a gas source and pump)-driven atomizerthat provides the atomization of the received melt 1304, as will beapparent to the skilled artisan in light of the discussion herein.

Of note, the fall chamber 1330 discussed herein may lead to preferredatomization techniques, as will be apparent to the skilled artisan. Byway of example, a centrifugal and/or a spinning/chopping disc or similaratomizer may produce strings of polymer material, and thus maynecessitate a wider fall chamber 1330, while such a design considerationfor the fall chamber 1330 may not be relevant for gas-driven directedatomization.

The atomized polymer melt 1304 a may include, such as within the melt1304 or added during the atomization process, the aforementionedreinforcements or additives. The atomized melt 1304 a may then “fall”through the powder processing fall chamber 1330, as illustrated. Assuch, the atomized melt 1304 a may comprise a suitable molecular weightand melt viscosity to successfully crystallize in a controlled amount oftime, i.e., to crystallize as the atomized melt “falls” through the fallchamber 1330 to the collection point 1336. It will be appreciated that,although the “fall” of the atomized melt 1304 a may be dependent solelyon gravity, other expedients or impediments to a gravity-based fall maybe provided. By way of example, the chamber 1330 may be pressurized, mayinclude one or more gas inlets or high pressure “blowers” or the like1340, such as to advance or retard the “fall” through the fall chamber1330.

The chamber 1330 is optimally sized and shaped so as to accommodate thefull spray of the atomizer 1320, such as subject to any spray controlsplaced on the atomizer 1320 for a given process. That is, the chamber1330 is sized and shaped so as to allow for controlled cooling of themaximum spray area for the atomized melt 1304 a as the particles of theatomized melt 1304 a fall/travel through the fall chamber 1330.

The fall chamber 1330 may comprise substantially uniform conditionsthrough the fall zone, such as with respect to temperature and pressure,or may comprise a plurality of processing zones 1336. By way of example,the chamber may comprise a series of heating or cooling zones 1340 a,1340 b, 1340 c, 1304 d . . . , such as may cool the melt in accordancewith a given control algorithm to obtain a desired final particle sizeand sphericity for produced print particle 12 from the provided atomizedpolymer melt 1304 a. To that end, the fall chamber 1330 may comprisenumerous heating or cooling elements 1340 a, 1340 b, 1340 c . . . alongthe vertical axis thereof, and/or may include a tuned gas flow asrequired to control the temperature of the fall chamber, and, moreparticularly, the melt 1304 a passing therethrough, at many points alongthe vertical axis of the fall chamber 1330. For example, one of thezones may hold the melt point of a particular polymer to build thecrystalline region, such as a hold temperature of between 50-300 degreesC., and more particularly 170-250 degrees C., and may then provide aseries of controlled cooling zones to solidify the crystallized polymerinto a dried powder particle 12.

The foregoing optimizes the control of the crystallinity and of otherproperties, such as the sphericity, of the polymer melt 1304 a as itcools or is affirmatively cooled through the fall chamber 1330. Thetuning and control, such as using the control algorithm 1190 discussedherein, of the polymer crystallization kinetics and/or of other powdercharacteristics allows for optimization for peak performance of theprint material 12 formed by the disclosed system and method in an AMprint process 14.

Thus, simply put, the chamber 1330 may provide a particular “fall” time,given the conditions in the chamber 1330. This fall time may or may notbe divided into a series of time horizons, such as wherein each horizoncomprises a fall time and temperature, such that the atomized melt ismodified during the fall in order to reach a desired physical state as apulverant/powder particle 12 upon reaching the collection point 1336.

As discussed, following the “fall” through the chamber 1330, collectionof powder 12 at collection point 1336 may occur, such as prior to or inconjunction with particle separation. For example, powder collection mayoccur into a collection chamber acting as collection point 1336, whichmay be located at the base of the fall chamber 1330, or which may beadjacent to the fall chamber 1330 such that the powder is blown, rolled,sucked, or similarly collected into the adjacent collection chamber1336.

Particle separation may separate the particles based on any knowncriteria, including, but not limited to, particle size, weight,sphericity, chemical makeup, or pursuant to other engineering designcriteria. Further, particle separation may occur via any knownmethodology, such as the use of air classifiers, cyclones, or the likewithin or otherwise in fluidic communication with collectionpoint/chamber 1336.

By way of non-limiting example, an air classifier 1350, which iscommonly employed in industrial processes in which a volume of mixedmaterials with differing physical characteristics needs to be separatedquickly and efficiently, may separate the powder 12 based on size,shape, or density, by way of non-limiting example. In such a case, thepowder 12 may be injected for sorting from collection point 1336 intoair classifier 1350, which may comprise a column of rising air. In theair classifier 1350, air drag on the powder 12 supplies an upward force,which counteracts the force of gravity and lifts the powder 12 to besorted. And, due to the dependence of air drag on each particle's sizeand shape, the powder particles 12 in the moving air column are sortedvertically and thereby separated.

Collection of only powder particles having the desired characteristics,such as the desired particle size range, provides for furtheroptimization of the powder collected as a print material 12 for use in aparticular AM process 14. Moreover, powder particles that fail to meetthe separation characteristics, such as being too large or too small,may be collected for re-melt into melt 1304, thus implementing a “zerowaste” process in certain of the embodiments.

As discussed throughout, the chamber 1330/300 may be horizontal orvertical. A vertical chamber may have material dropped from the topthereof through the chamber, or pushed/pumped up from the bottom, asdiscussed. A horizontal chamber may have material entry from the sides,and may include an “air table” to increase residence time in thechamber.

Feed material entered into the chamber may be in a filament form, or, insome embodiments, may be fed from an extruder. The extruder may be anyof various designs, may be horizontal or vertical in format to match thechamber design, and may operate at any temperature or other feedcharacteristics needed for each embodiment.

Controlled feedback loop of pressure at the atomizer feed nozzle (i.e.,a pressure transducer) and the pressure that which, for example, theextruder extrudes, allows for substantial control of incoming moltenpolymer pressure and flow rate. By way of non-limiting example, a screwextruder allows for optimal mixing, throughput and control of finalparticle size and characteristics.

Of course, extrusion may be used with or instead of various deliverymethods to the chamber. For example, to obtain molten polymer beads, alarge number of nozzles of a targeted length and diameter may be used toforce a polymer though the tube, the end/tip of which is designed toretain a particle until it is of sufficient mass that it overcomes thecapillary forces and falls free of the tube.

Increased residence time in the chamber may be provided by a gasinlet/gas flow from the bottom of the chamber, and, in some cases, alongthe chamber walls. This may be particularly the case in the instance ofa free-falling particle.

Further, rings/baffles/blades/steps/scoops (collectively “baffles”),i.e., a flow-directing or obstructing step, vane or panel, may beprovided on the chamber walls to not only control residence and falltime, but also to selectively control temperature, such as in zones orbands, among other functions. For example, the baffle may additionallybe used to capture material, such as to capture particles of a certainsize/density, and/or to increase residence time of a particle in thechamber, such as by redirecting airflow.

More particularly, steel or other material may be used to form thebaffle(s) that allow for a breakup in the gas flow path. This gas flowmodification may help to control temperature, capture material, orincrease residence time, as discussed throughout.

More particularly, and as illustrated in FIG. 4, a chamber 300 mayinclude a polymer or blend 304 input by an atomizer nozzle 302. Theatomized spray 304 may be flow directed and/or suspended by bothtemperature controlled gas flow inlets 306 at the base of the chamber,and/or temperature controlled gas flow inlets 308 providing flow 310from along the chamber sidewalls. Of note, gas inlets 306, 308 may bothcontrol flow/suspension, and at least partially control temperaturezones.

Chamber 300 may additionally include one or more baffles 312, which mayhelp to collect certain material and to control the flow direction andamount in the chamber. Material collection points 314 may collectmaterial desired to be collected from the chamber, such as based on thesettings of the flow volume, flow direction, temperature, and baffles,as discussed throughout.

A fritted, i.e., finely porous, mesh, filter or the like 330 may be usedto atomize the incoming polymer from nozzle 302. The fritted mesh may beused in conjunction with a high gas flow rate and high molten polymerpressure. Of course, in such cases, the skilled artisan will appreciatethat care need be taken to reduce the stringing/oozing that may occur.

The embodiments may additionally provide advantageous atomizationmechanisms 340 associated with nozzle 302 for spray 304. By way ofexample, a rotating blade or blades may atomize the polymer. Of course,a single blade may not have the energy required to fully atomize a highmolecular weight polymer. However the use of a multi blade design, whichmultiple blades may or may not counter rotate, and which may or may nothave some significant distance between the multiple blades, may remedyany issues experienced in a single blade embodiment.

Additionally in regard to the atomization nozzle, the embodiments maymake use of a gas flow in/from the center of the atomization nozzle, asdistinct from gas flow provided only along angles at the sides of thechamber. For example, molten polymer may exit a ring design of thenozzle, with a gas flow provided in the center of the nozzle exit ring.This gas flow may be in addition to gas flow along the sides of thechamber.

Now also with reference to FIG. 5, crystallization of the particle toobtain particular characteristics requires controlled heating, cooling,and thus flow of the particle, i.e., control in the changes of particletemperature over time. Therefore, the value in increasing/controllingthe particle residence time in the chamber 300 is the enhanced controlover the rate of the liquid

solid phase change that a molten polymer goes through. This increasedresidence time may be provided by a flow direction such that theparticles from atomizer nozzle 302 are suspended in a suspension 404.

If the polymer is given more time, or more controlled time, to orientits chains into the desired crystallinity, the material formed willperform better in powder bed fusion additive manufacturing processes, byway of non-limiting example. Moreover, by using either a free fall orgas suspension chamber system, or a combination thereof, the particlewill necessarily reduce its surface area, i.e., it will become morespherical. That is, the orientation of the chamber 300 or atomizer 302is not critical in the embodiments, so long as the requisite chambertime, temperature and flow for each particle are maintained.

Gas flow 306, 308 may be generated anywhere in, on or along the chamber,such as in order to control the residence time, such as in suspension404, and classification/collection 314, of the particles. For example,gas control 306 from the bottom of the chamber uses the differentialdensity of melt and the solid polymer to actively classify material. Byway of particular non-limiting example, using the combination of afluidized bed and/or suspension and/or a gravitational air classifier,the particles remain in a suspension of gas until the density of themolten particle increases enough (i.e., until it has cooledsufficiently) to fall from the suspension as solid particle 406 to becollected 314. However, finer particles 408 may be too light, and maythus be carried away for collection, such as by an alternative gas flow308. The gas inlets discussed herein may periodically pulse with morepressure/flow, thereby clearing the chamber of fine or solid desiredparticles, such as through an exit located above the suspension zone forcollection for fine particles, or at the base of chamber for desiredparticles.

The aforementioned fluidized bed/suspension additionally may be used toincrease residence time in the chamber. For example, a designed counterflow, such as an upward suspension flow, may be provided throughoutchamber. Accordingly, this suspension of particles may allow for theparticles to be held at certain temperatures for a desired residencetime, and then moved along through temperature bands at a controlledcooling rate throughout the chamber.

FIG. 6 shows a vessel 601 that can be utilized for forming polymermicrospheres. Polymer pieces, such as pellets, are heated to atemperature that allows them to flow and be forced through an atomizer602. A polymer extruder may provide melted polymer to atomizer 602. Thepolymer extruder may be a twin-screw extruder and may be controlled toachieve a set point pressure in the atomizer 602.

When using a polymer extruder to feed the atomizer 602, a homopolymermay be extruded into the atomizer 602. A benefit of using a polymerextruder to feed the atomizer 602 is that this configuration allowsadditives to easily be added to the polymer or polymers that are beingextruded. In this way, polymer(s) and additive(s) can be melted, mixed,atomized, and solidified in one system. This system could be used toproduce polymer spheres with additives encapsulated inside of them.Additives may comprise reinforcements and fillers such as fibers.Additives may comprise carbon fibers, glass fibers, inorganicreinforcements such as talc, glass beads, pigments, flame retardants,antioxidants, heat stabilizers, nucleating agents, and/or impactmodifiers.

Additives could be added at the extruder hopper or just prior to theatomization nozzle 602. The atomizer may force polymer through smallopenings, thereby causing them to exit the atomizer as small particles.To atomize the polymer, a fritted mesh or filter could be used inconjunction with a high gas flow rate and high molten polymer pressure.When using a fritted mesh or filter, pressurized polymer may be pushedthrough a very fine mesh and atomized polymer may exit the fritted meshor filter.

Rotating blades are another option for polymer atomization. One or morerotating blades may be used to atomize the polymer. When multiplerotating blades are used, the blades may be spaced at a fixed distanceapart from each other. The blades may rotate in the same direction asthe nearest blade(s) or they may counter-rotate. A rotating disc, suchas those used in glass fiber manufacturing, may be used to atomizepolymer.

Further, the atomizer may include adding a gas stream, such as nitrogen,either into the nozzle to mix with the polymer before the polymer exitsthe nozzle or the gas stream may be added separately and nearby thenozzle exit to create a zone of low pressure to pull small polymerdroplets into the vessel. Gas flow may also be added in the center of apolymer stream that is exiting the nozzle so that a gas flow is presentat a center of the polymer stream leaving the nozzle and a ring ofpolymer is present around the center gas flow leaving the nozzle.

To obtain molten polymer beads, a large number of tubular nozzles of atargeted length and diameter could be used. The end/tip of the tubescould be designed to retain a particle until the particle is ofsufficient mass to overcome the capillary forces holding the particle tothe tube. At this point, the particle would fall free of the tube. Tubescould be spaced apart to avoid collision.

The vessel may introduce a gas, such as nitrogen, tangentially into thevessel 601 to introduce a swirling flow around the perimeter of thevessel 601. The swirling flow could act to classify the falling polymerpellets. Larger and/or heavier polymer droplets would be pulled furtherto the outer perimeter and smaller and/or lighter polymer droplets wouldtend to stay towards the center of the vessel 101, per Stokes Law, whereV=settling velocity of the sphere, towards to outer perimeter (m/s),d=particle diameter (m), ρ₁=density of the particle (kg/m³), ρ₂=densityof the medium (kg/m³), r=radial distance from the center of rotation(m), ω=angular speed of rotation (revolutions per minute), andη=viscosity of the medium (kg/(m*s)):

$V = \frac{{d^{2}\left( {\rho_{1} - \rho_{2}} \right)}r\omega^{2}}{18\eta}$

The outward force acting on the polymer particles as they rotate aboutthe center axis of the vessel is a function of the particle's mass, theparticles tangential velocity, and the radial distance from the centerof vessel. This relationship is shown in the equation below.

$F_{c} = \frac{\left( {mv^{2}} \right)}{r}$

As shown in FIG. 6, various collection trays 603 a, 603 b, and 603 c canbe located at varying radial distances. Because there will be adistribution of particles, where heavier/larger particles are moreconcentrated at the outer perimeter of the vessel and lighter/smallerparticles are more concentrated towards the center of the vessel,positioning collection trays 603 a, 603 b, and 603 c as shown in FIG. 6would allow the collection of particles according to particlesize/weight. Alternatively, the vessel 601 in FIG. 6 could be conicallyshaped and polymer particles could be removed at various heights. Thisconical arrangement is also expected to separate particles by massand/or size. The topmost collection ports of the conical vessel would bemore concentrated in heavier/larger polymer particles and the lowermostcollection ports of the conical vessel would be more concentrated inlighter/smaller particles.

FIG. 6 also shows a separation device 604. A vacuum would pull gas andparticles through the separation device 604 to create a flow in thedirection shown by arrows in FIG. 6. The separation device may be acyclone. Clean gas, with a lower concentration of particles exits theseparation device at 605 and solids particles exit the separation device604 at 606. Separation device 604 may include an air lock 607 and acollection vessel 608. As shown in FIG. 6, a slip stream 609 of the gasbeing pulled through the bottom of the vessel may be directed to the topof the vessel to introduce a swirling, rotation flow inside of thevessel.

The time and temperature that polymer particles are exposed to willaffect their material properties, specifically because the amount ofcrystallinity in the polymer particles will vary as a function ofcooling time and cooling temperature(s). By controlling the time that ittakes for liquid polymer to change phase into a solid, the polymer'scrystallinity can be controlled. If a polymer is given more time toorient its chains, it will become more crystalline. A certain degree ofpolymer crystallinity is desirable when using polymer in a powder bedfusion additive manufacturing process. In order to control thecrystallinity in the solidified polymer microspheres, the temperatureand/or residence time of the polymer microspheres in the vessel may becontrolled. Temperature control may be accomplished by controlling thegas temperature in slip stream 609 and/or temperature control may beaccomplished by heating or cooling the vessel 601. Vessel temperaturecontrol may be accomplished by a heated and/or cooled jacketed vessel.Alternatively, electric heaters may be used to heat the vessel. Electricheaters may be located on the outer perimeter of the vessel 601 orimmersed within the vessel 601. Multiple heated and/or cooled sectionsmay be used to provide zones of different temperature.

A flow of gas (not shown) may be used to increase the residence timethat particles spend inside of the vessel. The gas that is used toincrease residence time would flow in the opposite direction thatmicrospheres are travelling. For example, if microspheres are fallingfrom the top of the vessel, gas would flow in an upward direction toincrease the amount of time that it takes for microspheres to travelfrom the atomizer to the bottom of the vessel. By using a free fall orgas suspension (or combination thereof), polymer particles will reducetheir surface area and become more spherical.

Further, baffles (represented as 610 a, 610 b, and 610 c in FIG. 6, butmay include any number of baffles) may be used to increase microsphereresidence time in the vessel. Baffles may be attached to the perimetersides of the vessel and may be straight or curved. Baffles may beslanted upward (from the vessel wall to the center of the vessel),downward (from the vessel wall to the center of the vessel), orhorizontal (from the vessel wall to the center of the vessel). Bafflesmay be made of steel or another material. Baffles may comprise rings,blades, or scoops and may allow for a breakup in the gas flow path tocontrol temperature, capture material, and/or to increase residencetime.

Once the print particles 12 are created, they may be printed using an AMprocess 14, as illustrated in FIG. 7. The AM printing process 14 may usea laser 504, and thus may be, for example, a dry blend SLS print. Insuch an embodiment, the particles 12 may also be dry blended withadditives 130, and the blended powder 120 may then be printed to a form16, layer-by-layer, using an SLS printer as discussed above.

Similarly, wherein the AM printing process is a powder bed fusionprocess, a single thin layer, such as an approximately 0.1 mm thicklayer, of compound print material 12 in powder 120, such as may becreated using the methodologies discussed above, may be spread over abuild platform. The laser 504 may then fuse the first layer, or firstcross section, of the model. Thereafter, a new layer of the compoundprint material 12 in powder 120 is spread across the previous layer,such as using a roller. Further layers or cross sections may then beadded until the entire model is created. Loose, unfused powder printmaterial may remain in position throughout, but may be removed duringpost processing, by way of non-limiting example.

Also in a manner similar to that of FIG. 7, binder jetting may use a“binder”, rather than or in addition to a laser 504. In such anembodiment, the powder print material 12 may be spread over the buildplatform, such as using a roller. A print head may then deposit a binderadhesive on top of the powder where required. The build platform maythen be lowered by the model's layer thickness. Another layer of powdermay then be spread over the previous layer, and the object is formedwhere the powder is bound to the liquid, layer-by-layer.

A multijet fusion methodology may operate in a manner similar to thepowder bed fusion, but may employ heat lamps or similar technologies,rather than a laser. Likewise, in a directed energy deposition AMmethod, an axis arm with a nozzle may move around a fixed object, andthe print material 12 may be deposited from the nozzle onto existingsurfaces of the object. The material may be provided, by way of example,in wire/filament or powder form, and may be melted for dispersal fromthe nozzle using a laser, electron beam or plasma arc.

Various other methodologies may provide a suitable format for the printparticles 12 to enable or improve printing using AM technologies. Forexample, a sheet may be made from the powder print materials, or afilament may be provided. Moreover, additives may be provided in theprint material to enable or improve printing and/or object formation.Additive materials may include, but are not limited to, hollow metaloxide beads or hollow polymeric spheres.

In each such embodiment, parameters of interest for the print material12 may include parameters such as moisture level, heat of build chamber,heater power and temperature emitted, time of heat exposure, timebetween layers, feed rate, feed temperature, pressure and vacuum, gasflow rate, and the like. In short, the core print particle 12 or anaspect thereof may melt, such as upon exposure to a laser, and thusfuses to nearby particles during an AM process. As such, the printmaterial 12 should be heated during the selected AM print process 14past its respective melting point. Under such circumstances, therespective polymer chains may suitably bond with those of the particlenext to each particle, to form output 16. The selected AM print process14 may allow that bond to cool, and thus the cooled particle chains forma solid layer in output 16. Of course, each print material 12 may alsobe subjected to additives 130 as discussed throughout, such as may aidwith melting or flow during melting, with impact resistance, or withheat stabilization, by way of example, dependent upon the AM processselected.

As such, an output part 16 processed as described herein may providecorrelated characteristics that are indicative of, and/or correlated to,the input material 12, and which occur pursuant to application of AMprocess 14, as described herein throughout. Such correlatedcharacteristics may be measured, by way of non-limiting example, byheat-flowing a sample of the input 12 and/or the output 16, and thenmeasuring thermal characteristics of the heat-flowed sample, such as Tm,Tg, Tcryst, heat of fusion, and the like. Likewise, infrared microscopymay allow for identification of the wavelengths of the correspondingchemical structures of the input material and/or the output objectlayers. Yet further, a thermogravimetric or similar analysis may beperformed on a sample of the input material 12 or printed output 16, andthis analysis may further include measurement of the composition ofdecomposition gases as the sample degrades, by way of example.

Of course, in view of the aforementioned prospective correlation ofcharacteristics between an input print material 12 and a printed outputobject 16, the correlated characteristics of output object 16 may varydependently not only in accordance with the input material 12, butadditionally based upon the process 14 employed to print the printmaterial 12 into the output object 16. Accordingly, one or morecomputing programs/algorithms 1190, such as may comprise one or more AMFfiles; one or more input material 12 and/or additive 130 choices; one ormore process 14 choices and/or one or more process characteristicschoices; and/or one or more output 16 shape, size, and/or characteristicchoices, may be executed by a computing system 1100. This execution mayoccur, for example, pursuant to an instruction to a GUI, such as toprovide a particular correlation as between an input material 12 and/oradditives 130 and a specific output object characteristic, and/or to usea particular available input material 12, using an available process 14,to target the ultimate production of a particular output object 16. Thisis illustrated with particularity in FIG. 8.

More particularly, FIG. 8 depicts an exemplary computing system 1100 foruse in association with the herein described systems and methods.Computing system 1100 is capable of executing software, such as anoperating system (OS) and/or one or more computingapplications/algorithms 1190, such as applications applying thealgorithms discussed herein, and may execute such applications 1190using data, such as materials and process-related data, which may bestored 1115 locally or remotely.

More particularly, the operation of an exemplary computing system 1100is controlled primarily by computer readable instructions, such asinstructions stored in a computer readable storage medium, such as harddisk drive (HDD) 1115, optical disk (not shown) such as a CD or DVD,solid state drive (not shown) such as a USB “thumb drive,” or the like.Such instructions may be executed within central processing unit (CPU)1110 to cause computing system 1100 to perform the operations discussedthroughout. In many known computer servers, workstations, personalcomputers, and the like, CPU 1110 is implemented in an integratedcircuit called a processor.

It is appreciated that, although exemplary computing system 1100 isshown to comprise a single CPU 1110, such description is merelyillustrative, as computing system 1100 may comprise a plurality of CPUs1110. Additionally, computing system 1100 may exploit the resources ofremote CPUs (not shown), for example, through communications network1170 or some other data communications means.

In operation, CPU 1110 fetches, decodes, and executes instructions froma computer readable storage medium, such as HDD 1115. Such instructionsmay be included in software, such as an operating system (OS),executable programs such as the aforementioned correlation applications,and the like. Information, such as computer instructions and othercomputer readable data, is transferred between components of computingsystem 1100 via the system's main data-transfer path. The maindata-transfer path may use a system bus architecture 1105, althoughother computer architectures (not shown) can be used, such asarchitectures using serializers and deserializers and crossbar switchesto communicate data between devices over serial communication paths.System bus 1105 may include data lines for sending data, address linesfor sending addresses, and control lines for sending interrupts and foroperating the system bus. Some busses provide bus arbitration thatregulates access to the bus by extension cards, controllers, and CPU1110.

Memory devices coupled to system bus 1105 may include random accessmemory (RAM) 1125 and/or read only memory (ROM) 1130. Such memoriesinclude circuitry that allows information to be stored and retrieved.ROMs 1130 generally contain stored data that cannot be modified. Datastored in RAM 1125 can be read or changed by CPU 1110 or other hardwaredevices. Access to RAM 1125 and/or ROM 1130 may be controlled by memorycontroller 1120. Memory controller 1120 may provide an addresstranslation function that translates virtual addresses into physicaladdresses as instructions are executed. Memory controller 1120 may alsoprovide a memory protection function that isolates processes within thesystem and isolates system processes from user processes. Thus, aprogram running in user mode may normally access only memory mapped byits own process virtual address space; in such instances, the programcannot access memory within another process' virtual address spaceunless memory sharing between the processes has been set up.

In addition, computing system 1100 may contain peripheral communicationsbus 1135, which is responsible for communicating instructions from CPU1110 to, and/or receiving data from, peripherals, such as peripherals1140, 1145, and 1150, which may include printers, keyboards, and/or thesensors discussed herein throughout. An example of a peripheral bus isthe Peripheral Component Interconnect (PCI) bus.

Display 1160, which is controlled by display controller 1155, may beused to display visual output and/or other presentations generated by orat the request of computing system 1100, such as in the form of a GUI,responsive to operation of the aforementioned computing program(s). Suchvisual output may include text, graphics, animated graphics, and/orvideo, for example. Display 1160 may be implemented with a CRT-basedvideo display, an LCD or LED-based display, a gas plasma-basedflat-panel display, a touch-panel display, or the like. Displaycontroller 1155 includes electronic components required to generate avideo signal that is sent to display 1160.

Further, computing system 1100 may contain network adapter 1165 whichmay be used to couple computing system 1100 to external communicationnetwork 1170, which may include or provide access to the Internet, anintranet, an extranet, or the like. Communications network 1170 mayprovide user access for computing system 1100 with means ofcommunicating and transferring software and information electronically.Additionally, communications network 1170 may provide for distributedprocessing, which involves several computers and the sharing ofworkloads or cooperative efforts in performing a task. It is appreciatedthat the network connections shown are exemplary and other means ofestablishing communications links between computing system 1100 andremote users may be used.

Network adaptor 1165 may communicate to and from network 1170 using anyavailable wired or wireless technologies. Such technologies may include,by way of non-limiting example, cellular, Wi-Fi, Bluetooth, infrared, orthe like.

It is appreciated that exemplary computing system 1100 is merelyillustrative of a computing environment in which the herein describedsystems and methods may operate, and does not limit the implementationof the herein described systems and methods in computing environmentshaving differing components and configurations. That is to say, theinventive concepts described herein may be implemented in variouscomputing environments using various components and configurations.

In the foregoing detailed description, it may be that various featuresare grouped together in individual embodiments for the purpose ofbrevity in the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that any subsequently claimedembodiments require more features than are expressly recited.

Further, the descriptions of the disclosure are provided to enable anyperson skilled in the art to make or use the disclosed embodiments.Various modifications to the disclosure will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other variations without departing from the spirit orscope of the disclosure. Thus, the disclosure is not intended to belimited to the examples and designs described herein, but rather is tobe accorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. An apparatus for forming print material particlesfor additive manufacturing (AM) printing, comprising: a melt chambercomprising a polymer melt; an atomizer that atomizes the polymer meltand that distributes the atomized polymer melt; a fall chambercomprising a plurality of zones into which the atomized polymer melt isdistributed; a plurality of heating and cooling elements selectivelyvaried along a vertical axis of the fall chamber and along the wallsthereof by at least one controller to provide the plurality of zones,including at least one zone having a hold temperature of 170-250 degreesCelsius to build crystallinity of the atomized polymer melt, and whichprovide a flow of the distribution of, to thereby provide a variedseries of controlled modification horizons including a sphericityhorizon to, the atomized polymer melt along the vertical axis as theatomized polymer melt falls along the vertical axis; the controllercontrolling also at least partially controlling the atomized polymermelt to provide a requisite time, temperature and flow of the atomizedpolymer melt to provide particular characteristics to the print materialparticles in each of the controlled modification horizons; and a firstcollector to receive the print material particles formed from theatomized polymer melt after falling through the plurality of zones. 2.The apparatus of claim 1, wherein the atomizer comprises a high-pressurenon-reactive gas jet.
 3. The apparatus of claim 2, wherein thenon-reactive gas comprises nitrogen gas.
 4. The apparatus of claim 2,wherein the high pressure comprises about 1050 psi.
 5. The apparatus ofclaim 1, wherein the print material particles range in size from about0.1 μm to about 200 μm.
 6. The apparatus of claim 1, wherein theatomized polymer melt is polyethylene-based.
 7. The apparatus of claim1, wherein the collected print material particles comprise a powderhaving a size of about 0.1-200 μm.
 8. The apparatus of claim 1, whereinthe atomized polymer melt comprises about a 3.175-mm melt stream size.9. The apparatus of claim 1, further comprising a feeder to the meltchamber, wherein a polymer in the feeder comprises pellets.
 10. Theapparatus of claim 1, wherein the print material particles are powderbed fusion AM particles.
 11. The apparatus of claim 1, wherein theheating elements comprise electric heaters.
 12. The apparatus of claim1, further comprising at least two gas inlets, each to further controlat least a flow and a temperature in each of the plurality of zones. 13.The apparatus of claim 1, wherein the atomized polymer melt includes anucleating agent.
 14. The apparatus of claim 1, wherein the atomizedpolymer melt comprises non-polymer additives.
 15. The apparatus of claim14, wherein the additives comprise at least one of an alloy and areinforcement.
 16. The apparatus of claim 1, wherein the atomizercomprises one of a centrifugal, a chopping disc, and a gas atomization.17. An apparatus for forming print material particles for additivemanufacturing (AM) printing, comprising: a melt chamber comprising apolymer melt; at least one capillary tube that releases portions of thepolymer melt when capillary forces of the capillary tube are overcome; afall chamber comprising a plurality of zones into which the releasedpolymer melt is distributed; a plurality of heating and cooling elementsselectively varied along a vertical axis of the fall chamber and alongthe walls thereof by at least one controller to provide the plurality ofzones, and which provide a flow of the distribution of, the releasedpolymer melt along the vertical axis as the released polymer melt fallsalong the vertical axis; the controller controlling also at leastpartially controlling the released polymer melt to provide a requisitetime, temperature and flow of the released polymer melt to provideparticular characteristics to the print material particles in each ofthe plurality of zones; and a first collector to receive the printmaterial particles formed of the polymer melt after falling through theplurality of zones.
 18. The apparatus of claim 17, wherein the at leastone capillary tube comprises more than one capillary tube.
 19. Theapparatus of claim 17, further comprising at least two gas inlets, eachto further control at least the flow and the temperature in each of theplurality of zones.
 20. The apparatus of claim 17, wherein the printmaterial particles range in size from about 0.1 μm to about 200 μm.